1. Field of the Invention
This invention relates to solar batteries of the type having spherically-shaped cells. The invention is also directed to a method of forming a solar battery assembly.
2. Background Art
In a conventional solar battery, an internal electrical field is generated between P-N connecting members of a semiconductor layer. Impingement of light upon the solar battery develops electron/electron hole pairs. The electrons collect on the N side, with the electron holes formed on the P side. With an external load connected, electric current flows from the P side toward the N side. Through this process, solar batteries are able to convert light energy into useable electrical energy. In recent years, solar batteries have been made using spherical semiconductors. The spherical semiconductors may be monocrystal or polycrystal silicon, typically with a diameter of less than 1 mm.
An example of a conventional solar battery using spherical semiconductors is described in Kokai 6-13633 and shown in FIG. 1, herein, at 10. The solar battery 10 consists of an array of spherical semiconductors 12 which are connected together utilizing a conductive board 14, which in this case is shown to be aluminum foil, or the like. Each of the spherical semiconductors 12 has a primary conductive skin 16 which envelops a secondary conductive core 18. The spherical semiconductors 12 are placed in an opening 20 in the conductive board 14 so as to project from opposite sides 22 and 24 of the board 14. A portion of the skin 16 is removed from the spherical semiconductor 12 on the side 24 of the board 14. An insulating layer 26 is formed against the core 18 which is exposed where the external skin 16 is removed. A portion of the core 18 and insulating layer 26 is removed at 28 so as to form a flat surface 30 which can be connected to a secondary conductive member 32, which in this case is aluminum foil. The surface 30 is connected in a high quality, ohmic manner to the conductive member 32.
It is difficult to maintain a precise relationship between the semiconductors 12 and the conductive board 14, insulating layers 26, and secondary conductive member 32 throughout the entire area of the solar battery 10, particularly with the spherical semiconductors 12 in a high density arrangement. Variation in the relationship of these elements may alter the operating characteristics of the semi conductors 12 and the performance of the battery 10.
Further, the manufacture of the solar battery 10 may involve multiple steps and processes. Manufacture may thus be relatively complicated. As a result, the costs attendant such manufacture may also be high.
Further, in forming an electrode, a contact terminal is needed for both the primary conductive skin 16 and the secondary conductive member 32. With the light receiving area being decreased, it may be difficult to construct an effective contact terminal.
In one form, the invention is directed to a method of forming a solar battery assembly. The method includes the steps of: providing a plurality of spherically-shaped cells, each having a semiconductor layer and an outer electrode layer; forming a solder layer between the plurality of spherically-shaped cells so as to maintain the plurality of spherically-shaped cells in a desired relationship; removing a part of the outer electrode layer to expose a part of the semiconductor layer; and placing an inner electrode in contact with the exposed part of the semiconductor layer.
The method may further include the step of preliminarily maintaining the plurality of spherically-shaped cells in the desired relationship before forming the solder layer.
In one form, each of the plurality of spherically-shaped cells in the desired relationship has a top side and a diametrically opposite bottom side and the step of preliminarily maintaining the plurality of spherically-shaped cells in the desired relationship involves applying an adhesive layer to the top sides of the plurality of spherically-shaped cells.
The method may further include the step of aligning the plurality of spherically-shaped cells in the desired relationship on a tray surface before applying the adhesive layer.
The method may further include the steps of inverting the adhesive layer with the plurality of spherically-shaped cells adhered thereto into a soldering orientation in which the bottom sides of the plurality of spherically-shaped cells are exposed and above the top sides of the plurality of spherically-shaped cells.
The step of forming a solder layer may involve sprinkling solder particles over the plurality of spherically-shaped cells and into a space between the adhesive layer and the plurality of spherically-shaped cells with the adhesive layer and the plurality of spherically-shaped cells adhered thereto in the soldering orientation.
The step of forming a solder layer may further involve the steps of liquefying the solder particles in the space between the adhesive layer and the plurality of spherically-shaped cells and thereafter solidifying the liquefied solder particles so that the solder layer connects between the plurality of spherically-shaped cells.
The method may further include the steps of removing at least a part of the adhesive layer and etching the solder layer from the bottom sides of the plurality of spherically-shaped cells.
The step of removing a part of the outer electrode layer may involve using the solder layer as a mask while removing the part of the outer electrode layer.
The semiconductor layer may include a P-type layer and an N-type layer. The method may further include the step of removing a part of one of the N-type and P-type layers to expose a part of the other of the N-type and P-type layers. The step of placing the inner electrode in contact with the exposed part of the semiconductor layer may involve placing the inner electrode in contact with the part of the other of the N-type and P-type layers.
The outer electrode layer may be a transparent conducting film over the semiconductor layer.
The step of placing the inner electrode in contact with the exposed part of the semiconductor layer may involve fixing a conductive sheet defining the electrode to the plurality of spherically-shaped cells to thereby maintain the plurality of spherically-shaped cells fixedly in the desired relationship.
The method may further include the step of forming an insulative layer on the conductive sheet between the plurality of spherically-shaped cells to thereby insulate the inner electrode from the outer electrode layer.
The method may further include the step of impregnating the exposed part of the semiconductor layer with impurities before placing the inner electrode in contact with the exposed part of the semiconductor layer.
The method may further include the step of applying an insulative material to the solder layer after etching the solder layer and before removing the part of the outer electrode layer to expose a part of the semiconductor layer.
The step of applying an insulative layer may involve applying an insulative layer that is a low viscosity insulating resin.
The insulative layer may be applied as a film, as by spin coating.
In one form the plurality of spherically-shaped cells are in contact with each other with the spherically-shaped cells in the desired relationship.
Each of the plurality of spherically-shaped cells may have a spherical core over which the semiconductor layer is applied.
The spherical core may be made from an insulative material. Alternatively, the spherical core may be made from metal, which may be in electrical contact with the inner electrode.
One of the N-type and P-type layers may be defined by a spherical core.
In one form, the solder layer electrically connects between the outer electrodes of the plurality of spherically-shaped cells.
The invention is also directed to a solar battery having a plurality of cells, a conductive layer fixed to the plurality of cells, and a solder layer. The cells each have a semiconductor layer and an outer electrode layer. The semiconductor layer has a P-type layer and an N-type layer, with there being a part of one of the N-type and P-type layers exposed through the outer electrode layer. The conductive layer is fixed to the plurality of cells in contact with the exposed part of the one of the N-type and P-type layers. The solder layer extends between the conductive layer and the plurality of cells so as to electrically connect between the outer electrodes of the plurality of cells. The solder layer is electrically insulated from the conductive layer.
The plurality of cells may be spherically-shaped cells.
In one form, the outer electrode layer is a transparent conducting film.
The solar battery may further include an insulative layer on the solder layer between the solder layer and the conductive layer.
In one form, one of the P-type and N-type layers is a silicon sphere and the other of the P-type and N-type layers is a silicon layer on the silicon sphere.
Each of the plurality of cells may have a metal core. The metal core may be spherically shaped. In one form, the metal core is exposed through the semiconductor layer and in electrical contact with the conductive layer.
The semiconductor layer may be formed around the metal core.
The solar battery assembly may further include an insulative layer over the conductive layer which electrically insulates the outer electrode layers from the conductive layer.